In general, polyimide resins have a high heat resistance and excellent electrical insulation, and thus are utilized as a printed circuit board and heat-resistant adhesive tape material. In the form of resin varnishes, they are also utilized as surface protection films and interlayer dielectrics for electrical components and semiconductor materials. However, because polyimide resins dissolve only in limited solvents, the method typically used is to apply polyamic acid, which is a polyimide precursor that dissolves with relative ease in various organic solvents, onto a substrate and then subject the polyamic acid to cyclodehydration by high-temperature treatment, thereby obtaining a cured product made of polyimide resin.
In contrast, methods for obtaining a cured polyimide resin using ultraviolet light or visible light proceed at low temperature and in a short time, and so there exists an increased demand for adhesives and coating agents obtained by UV curing polyimide resins (Patent Document 1). Also, thixotropy is desired in order to discourage liquid sag and prevent stringing during application as an adhesive or a coating agent, and to keep a glob of applied material from spreading. Moreover, in the bonding of vehicle-mounted objects in transport equipment such as automobiles, airplanes and ships, when the cured adhesive is hard, problems such as vibration-induced peeling and cracking sometimes arise, and so a storage modulus and good adhesiveness capable of withstanding vibrations is desired.